The present invention relates to a method for the separation of minerals from an ore. More particularly, it relates to a method of separating the components of an ore by distinguishing between a difference in color provided to the particular ore components due to their differing surface chemical properties. This invention further relates to a method of separating limestone from limestone ore containing iron-bearing rock, chert, granite, quartz, and other silicates.
Current methods of optically sorting minerals from the ore in which they are contained utilize the naturally occurring differences in color or reflectivity of the various components of an ore. Using this naturally occurring difference in coloration, the components of the ore can be separated by optical sorting techniques. However, some problems are presented with such current optical sorting techniques. One problem encountered in separating the components of an ore is the occurrence of a range of colors for a valuable mineral component of the ore. Such a range of colors for the valuable mineral component of an ore can overlap a range of colors for the nonvaluable components e.g. both limestone and quartz can be essentially of the same color and reflectivity. In the optical sorting of the various components of an ore, in reliance upon the naturally occurring differences in color and reflectivity, some of the nonvaluable components are sorted along with the valuable mineral components and some of the valuable mineral components are discarded as gangue.
Further, when there is an overlap of the range of colors and reflectivity for the valuable and nonvaluable mineral components there is a sacrifice of percent yield when purity of the valuable component is desired and correspondingly there is a sacrifice of percent purity when a high yield of valuable component is desired.
Another disadvantage of optically separating components of a mineral ore by the naturally occurring differences in color or reflectivity of the individual components is that such a separation method is limited to use on only those mineral ores wherein the individual components exhibit such a substantially noticeable difference in color or reflectivity.
Separating mineral components by their naturally occurring differences in color or reflectivity is currently conducted by sorting the various components by hand or machine which senses visible light. Such sorting is limited to the ability of the individual to discern optical differences such as colors and/or reflectivity. Hand sorting of the components of the mineral ore is typically a job for unskilled labor. Due to this level of skill of the laborer and the tediousness of the job, there is generally a high turnover rate for such hand-sorting operations. Unfortunately, the ability to separate the components of an ore by hand-sorting techniques requires extensive training of the individuals conducting the hand sorting in order to obtain products of value from the operation.
It is the general practice to separate limestone from the other components present in limestone ore by methods that distinguish between the physical properties of the limestone and such other components. The term "gangue" will be used hereinafter to refer to the nonvaluable components present within an ore. For example, the nonvaluable mineral components comprising gangue from a limestone containing ore are impurities such as chert, iron-bearing rock, granite, quartz, and various other silicates. The methods used to separate limestone from gangue present in limestone ore include hand-sorting or other optical sorting methods. Hand-sorting is slow and tedious and is economically unattractive. The other optical sorting methods are limited because of difficulty in the resolution of colors and reflectivity and the difficulty of distinguishing among the various shades of colors and reflectivity presented by the limestone and gangue in the ore. In particular, limestone and quartz present in limestone ore are difficult to optically separate due to their similarity in color as both components are generally white or grey in color.